Friction welding with conoids

ABSTRACT

A joining process and friction welded structure is disclosed, including a first member with a conoid recess, and a second member with a second conoid tip that is friction welded to the recess in the first member. One, or both, of the conoids may be a non-spheroid, such as a paraboloid. In addition, the conoid recess may have a vertex angle that is greater than a vertex angle of the conoid tip.

TECHNICAL FIELD

[0001] The technology described here generally relates to fusion bondingusing dynamic frictional energy and, more particularly, friction weldingby rotating one work surface relative to another about an axis.

BACKGROUND

[0002] Friction welding is a process in which metals, and/or othermaterials, are joined by heat which is generated when the parts arerubbed together under high pressure. The advantages of friction weldinginclude very rapid completion rates, good mechanical properties, and theelimination of the need for shielding gases under most circumstances.There are at least twenty variants of friction welding processes. Someof those variants include rotary friction welding, friction studwelding, radial friction welding, linear friction welding, orbitalfriction welding, third-body friction welding, and friction taper plugwelding.

[0003] Friction stir welding is a relatively new friction weldingprocess. It involves rotating a small tool between two closely-buttedcomponents. Frictional heating causes the materials in the components tosoften and the forward motion of the tool forces material from the frontof the tool to the back, where it consolidates to form a solid stateweld. Stir welding processes thus combine the flexibility of mechanizedarc welding with the desirable results of friction welding.

[0004] Friction stir welding has been used to join various materialsthat will soften and co-mingle under applied frictional heat, includingas metals and plastics. For example, U.S. Pat. No. 5,975,406, filed Feb.27, 1998 by Mahoney et al. (and assigned at issuance to the BoeingCompany) discloses a method to repair voids in aluminum alloys, and isincorporated by reference here in its entirety. As reproduced in FIG. 1of the present application, an aluminum work piece 30 with an anomalyvoid is machined in order to provide a tapered bore 34 with grooves andridges 36 provided on the surface of the bore. A consumable tapered plug38 is then inserted into the tapered bore 34 with a larger section 40connected to a rotating motor (not shown).

[0005] As shown in FIG. 2, the included angle cc of the tapered bore 34is preferably greater than the included angle of the tapered plug 38 inorder to ease rotation of the tapered plug, and to prevent air frombeing between the tapered plug, tapered bore, and/or tapered ridges 36.Until now, however, the shapes of the tapered plug 38 and tapered bore34 have not been adequately considered with regard to friction stirwelding and/or other friction welding processes.

SUMMARY

[0006] These and other drawbacks of conventional technology areaddressed here by providing a joining method and friction weldedstructure including a first member with a conoid recess, and a secondmember with a second conoid tip that is friction welded to the recess inthe first member. One, or both, of the conoids is preferably anon-spheroid, such as a paraboloid. In addition, the conoid recesspreferably has a vertex angle that is greater than the vertex angle ofthe conoid tip.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The various embodiments will now be described with respect to thefollowing figures, where the reference numerals have been consistentlyused to identify the same features in each of the drawings, and

[0008]FIG. 1 is a schematic illustration of a conventional frictionwelding procedure;

[0009]FIG. 2 illustrates the included angle from FIG. 1;

[0010]FIG. 3 is a cross-sectional illustration of a friction weldingstructure.

[0011]FIG. 4 is a software code listing for a friction welding model;and

[0012]FIG. 5 is a plot of data from the software shown in FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Conic sections, or “conics,” are some of the oldest curves to bemathematically studied. Conics are formed by the intersection of a rightcircular cone and a plane. The cone may have any vertex angle; however,it is the angle of intersection between the cone and the plane thatdetermines whether the resulting curve is an ellipse, parabola, orhyperbola.

[0014] In mathematical terms, conics can be defined as follows: Given a“directrix” line D, and a “focus” point F not on D, a conic is the locusof points P such that the distance from P to F divided by the distancefrom P to D is a constant referred to as the “eccentricity.” If theeccentricity is equal to 1, the resulting conic is a parabola, whileeccentricities less than 1 result in an ellipse and eccentricitiesgreater than 1 result in a hyperbola.

[0015] A solid formed by the revolution of a conoid about its axis isreferred to as a “conoid.” If the conoid is a parabola, the resultingsolid is a parabolic conoid or “paraboloid.” Similarly, if the conoid isa hyperbola, then the solid is referred to as a hyperbolic conoid, or“hyperboloid,” while an ellipse forms an elliptic conoid, also known asan “ellipsoid,” or a spheroid. The term “conoid” is used here to includetruncated conoids, and/or other partial conoids, including conoidshaving incongruous portions near zones of high curvature. “Non-spheroidconoid” is used here to refer to ellipsoids, paraboloids, hyperboloidsand/or portions thereof.

[0016]FIG. 3 is a cross-sectional view of a friction welding structure300. The structure 300 includes a first member 320 having a conoidrecess 322 formed therein. The recess 322 is preferably a non-spheroidconoid and, more particularly, a paraboloid. A second member 340 isarranged in the recess 322. The second member 340 includes a conoid tip342. The tip 342 is also a non-spheroid conoid and preferablycorresponds to the shape of the recess 322. For example, since therecess 322 is a paraboloid, the tip 342 is also illustrated as aparaboloid. Furthermore, the paraboloid recess 322 has a vertex anglethat is substantially the same as, or preferably greater than, thevertex angle of the paraboloid tip 342. The second member 340 alsoincludes an optional base 344 for securing the second member 340 to arotating driver. For example, the base 344 may be a cylindrical shankfor mounting in a chuck.

[0017] During the friction welding process, the second member 340 isinserted into the recess 322 in the first member 320. Typically, a smallgap will be formed between the sides of the first and second members320, 340. The first and second members 320, 340 are then rotatedrelative to each other so that frictional heat is created at the pointof contact between the end of the tip 342 and the base of the recess322. The contact initially occurs at the deepest point in the recess 322and then proceeds outward as the material from the second member 340forges its way into the material of the first member 320. The vertexangle difference between the conoid recess 322 and the conoid tip 342ensures that the tip of the first member 340 will displace all, or most,of the air contained in the recess 322 during the welding process.

[0018] A paraboloid recess 322 and paraboloid tip 342 are preferred inorder to provide an evenly distributed weld energy over the surface ofthe tip. This even distribution provides improved efficiency and weldproperties, especially when joining dissimilar materials such as analuminum first member with a copper second member. For example, thesematerials are often used in order to provide a copper heat sink in analuminum housing for integrated circuits as in Agilent Technologies'“Articooler” family of products. This preferred shape was determinedusing the computer simulator technology described in more detail below.

[0019] Further practical considerations often require the end of the tip342 to be truncated, preferably in a plane that is substantiallyperpendicular to the longitudinal (vertical in FIG. 3) axis of the tip.Flattening the end of the tip 342 in this manner allows the tip to bemore stably positioned in a flat-bottomed hole prior to spinning.Similarly, a conic, or otherwise pointed, tip may also be used in aflat-bottomed or correspondingly-shaped recess for stabilizing the tip.Furthermore, it can be difficult to accurately form a conoid profilewith a small diameter near the end of the tip. Therefore, the highlycurved end of the tip 342 may vary from the preferred conoid form asdictated by the need for stability, manufacturability, and/or otherconsiderations without significantly departing from the function andresult of the technology disclosed here.

[0020]FIG. 4 is a computer code listing 400 for a friction welding modelthat can be executed with the “Engineering Equation Solver” (EES)software available from F-Chart Software of Middleton, Wis. The modelstarts with the weld parameters listed at the top of the page; namely,that the tip 342 (FIG. 3) is secured to a flywheel having a moment ofinertia equal to 1.62 ft-lb² and rotating at 3200 rpm. The model assumesthat the tip 342 will be forced into the recess 322 (FIG. 3) with anormal force of 4540 lbs so that it will come to rest in about 0.5seconds.

[0021] The EES software solves the unbracketed equations in lines 1-8,10-11, 13 and 15-18 of the code 400 for the radius “radj” of the tip 342(in meters) for the distance “htot” (also in meters) from the (bottom inFIG. 3) end of the tip 342, where

[0022] “F” is the compressive force (in Newtons);

[0023] “ro” is the largest outer radius of the tip (in millimeters);

[0024] “mu” is the sliding coefficient of friction between the tip andbase (dimensionless);

[0025] “omega” is the angular velocity of the tip (in radians persecond);

[0026] “Pfr” is the power dissipated by friction at the edge of the tip(held constant at 10.15 kilowatts);

[0027] “r” is the distance from the longitudinal (vertical in FIG. 3)axis of the tip (in meters); and

[0028] “theta” is the angle of the curve formed at the edge of the tip(in radians, from vertical in FIG. 3).

[0029] The bracketed information including, the equations in lines 3,12, and 14, does not form part of the calculation. However, theseportions of the model may be un-bracketed in order to further constrainthe model.

[0030] The output of these solutions is shown in the plot 500 in FIG. 5where the vertical axis is the distance (in meters) from the lower endof the tip 342 (in the orientation shown in FIG. 3) and the horizontalaxis shows the radial distance (also in meters) from the longitudinal(vertical in FG. 3) axis of the tip 342. In other words, the plot 500shows various half-profiles for the tip 342 if it were rotated 180° fromthe orientation shown in FIG. 3. Curve 502 illustrates the results forthe data shown in FIG. 4 while curves 504-510 illustrate results forother weld parameters; such as lower compressive forces, slower rpm,less friction, and/or higher weld dissipation energies.

[0031] In FIG. 5 each of the curves 502-510 moves to a value of zeroheight at some radius that is greater than zero. It is expected that,with lower values of weld dissipation energy, the curves 502-510 couldbe more accurately determined to have non-zero values for small radiusvalues. Nonetheless, this aspect of the plot 500 further illustrates thedifficulty associated with precisely describing and/or forming the endof the tip 342 so as to provided constant power dissipation near thecenter of the tip. Similarly, the plot 500 illustrates how the end ofthe tip 342 may be truncated, or otherwise incongruously formed withoutsignificantly affecting the function or result provided by thistechnology provided by constant weld power dissipation along theremainder of the tip.

[0032] When conventional curve-fitting techniques are applied to thecurves 502-510 shown in FIG. 5, it was found that parabolic curvesprovide the closest matches for values of height that are greater thanzero. It can therefore be concluded from the results of the simulationthat the optimum profile of the tip 342 is a parabola for most weldparameters. Since the profile is presumed to be the same for allpositions around the rotating tip, the optimal shape for the tip can becan extrapolated to a three-dimensional paraboloid. Furthermore, due tothe geometric relationship between parabolas and other conic sections,it is expected that similarly useful results (though not necessarilyoptimum power dissipation) will occur for other conoid shapes, andespecially non-spheroid conoids.

[0033] The technology described above has been found to provide completeair elimination and low resistivity at the weld function. In addition,these techniques provide better mechanical properties and higherproduction notes compared to conventional butt welding and solderingtechnologies.

[0034] It should be emphasized that the embodiments described above, andparticularly any “preferred” embodiments, are merely examples of variousimplementations that have been set forth here to provide a clearunderstanding of various aspects of the invention. One of ordinary skillwill be able to alter many of these embodiments without substantiallydeparting from scope of protection defined solely by the properconstruction of the following claims.

1. A friction welded structure, comprising: a first member with a firstconoid recess; and a second member, with a second conoid tip, frictionwelded in the recess of the first member. 2 The structure recited inclaim 1, wherein the tip is rotary friction welded in the recess.
 3. Thestructure recited in claim 1, wherein first and second conoids arenon-spheroid conoids. 4 The structure recited in claim 1, wherein thefirst and second conoids are paraboloids.
 5. The structure recited inclaim 1, wherein the first and second conoids have different vertexangles.
 6. The structure recited in claim 3, wherein the first andsecond conoids have different vertex angles.
 7. The structure recited inclaim 4, wherein the first and second conoids have different vertexangles.
 8. The structure recited in claim 5, wherein the vertex angle ofthe first conoid is greater than the vertex angle of the second conoid.9. The structure recited in claim 6, wherein the vertex angle of thefirst conoid is greater than the vertex angle of the second conoid. 10.The structure recited in claim 7, wherein the vertex angle of the firstconoid is greater than the vertex angle of the second conoid.
 11. Ajoining method comprising the step of friction welding a member with afirst conoid tip in a second conoid recess of another member.
 12. Themethod recited in claim 11, wherein the friction welding step includes arotary friction welding step.
 13. The method recited in claim 11,wherein first and second conoids are non-spheroid conoids.
 14. Themethod recited in claim 11, wherein the first and second conoids areparaboloids.
 15. The method recited in claim 11, wherein the first andsecond conoids have different vertex angles.
 16. The method recited inclaim 13, wherein the first and second conoids have different vertexangles.
 17. The method recited in claim 14, wherein the first and secondconoids have different vertex angles.
 18. The method recited in claim15, wherein the vertex angle of the first conoid is greater than thevertex angle of the second conoid.
 19. The method recited in claim 16,wherein the vertex angle of the first conoid is greater than the vertexangle of the second conoid.
 20. The method recited in claim 17, whereinthe vertex angle of the first conoid is greater than the vertex angle ofthe second conoid.